For debugging with GDB we have these alternatives:

• Debugging x86-32 Native Client Modules with nacl-gdb
• Debugging x86-64 Native Client Modules with nacl64-gdb (experimental)
• Limited debugging in x86 Native Client using regular (host) GDB (both 32 bit and 64 bit)
• GUI debugging x86-32 NaCl applications within chrome (experimental, uses GDB internally. Note: you will need a 32 bit chrome to try this)
• Remote Debugging With the Debug Stub
• Debugging a trusted plugin on Mac
• Debugging a trusted plugin on Windows